In general I feel that most of 'our' words are artificial constructs, most being bastardizations of Greek and Latin, or Latin endings tacked on to proper nouns, and as such pronunciation is arbitrary as long as everyone knows what's being talked about. I just wondered about this one. It's such a strange word, and not in any dictionary I can find, although defined as 'evergreen' in an online list of botanical epithets. If it's Greek, I wonder if the second part would be two syllables, "oh-on". "Zoon" seems unlikely. Whether the beginning is "ay" or "eye" might be a matter of taste.